1. Field of the Invention
This invention relates to an integrated circuit and its connecting circuit characterized by a terminal structure of a balancing operating high frequency integrated circuit and its internal connection and also characterized by a connecting method with the other same kind of the integrated circuit.
2. Description of the Related Art
With the recent development of semiconductor devices, high frequency circuits of VHF bands and UHF bands tend to be made integrated circuits.
There is a case that a high frequency circuit is formed of a first integrated circuit (mentioned as an IC hereinafter) forming, for example, a PLL-FM demodulating circuit and a second IC forming a differential type high frequency amplifying circuit. In such case, the first IC has a high frequency signal input terminal and a demodulating signal output terminal and has within the IC a demodulating circuit by a PLL including a voltage controlled oscillator (mentioned as a VCO hereinafter) and phase comparator. The above mentioned input terminal makes a balanced input and the output terminal makes a balanced output. Also, the second IC has an input terminal of a balanced input and an unbalanced output terminal.
The input signal for the first IC is fed to the balanced input terminal of the first IC, for example, through a balance-unbalance converting balloon transformer or the like.
The first IC has also a terminal for connecting a tank circuit to a VCO, terminal for grounding and terminal for a power source.
The signal from the balanced output terminal of the first IC is led to the balanced input terminal of the second IC, for example, through a lag type lead filter.
The second IC balances and amplifies the input signal and leads an unbalanced output out of the output terminal. This second IC also has an grounding terminal and power source terminal.
As mentioned above, in making a high frequency circuit an IC, the interior of the IC fundamentally takes the fomation of a differential amplifier but the high speed device to be used for this is so low in the pressure-resistance that a low voltage source is used and therefore the input-output dynamic range of the IC can not be made high. Therefore, the IC formed of a differential amplifier is adapted to the balancing operation. On the other hand, the circuit (for example, the balloon transformer input winding or lead filter) externally connected to the IC is generally used in the unbalancing operation.
When the high frequency grounding surface is made large, the grounding potential will be reduced and the noise induction to the signal line from the above mentioned power source line or the like will reduce but, within the IC, the grounding surface is so small that the reduction of the grounding potential is almost impossible. Therefore, in the IC, there is made a method of removing the same phase noises by balancing operating the circuit. If the circuit is not operated to be balanced but is forcebly operated to be unbalanced by grounding one of the balanced input terminals of the IC, an amplitude twice as large as in the case of the balancing operation will be required and therefore the input dynamic range will be a problem. Also, there will be a disadvantage that the bonding wire or the like within the IC at the other input terminal that is grounded will have a new impedance and the induction amount from the grounded terminal will become large.
Now, the balancing operating circuit has the above mentioned effect but can not remove the noise caused by the induction between the signal terminals. Therefore, for example, a vacant terminal is provided between the balanced input terminals so that the induction between the signal terminals may be reduced or the distance between the balanced output terminals of the IC is made large to separate the input or output terminals of the IC from each other.
However, if such vacant terminal is made, though the circuit is made an integrated circuit and the integrated degree is elevated, the number of the terminals will increase, the package size will become large and the other functions will be restricted to be mounted.
Also, when a multi-terminal package is used, the lengths of the internal bonding wires from such respective terminals as the grounding terminal, voltage source terminal and signal terminal to the chip within the IC will become so large as to deteriorate the high frequency characteristic and, as the respective lengths are different, the effect of the balancing operation to eliminate the same phase induction noises (from the power source line or the like) will reduce.
As explained above, in the conventional high frequency integrated circuit, a vacant terminal is provided between two signal terminals for a balancing operation so that the induction between the signal terminals may be reduced. In consideration of the lengths of the respective bonding wires from the respective signal terminals and grounding terminal to the internal chip, there have been problems that, as the lengths are respectively different, the high frequency characteristic will deteriorate, the same phase induction noise will not be well eliminated and the number of the terminals will become large.